1. Field of the Invention
The present invention relates to a method of diagnosing the deterioration of insulating paper used in an oil-filled electric apparatus such as an oil-filled transformer, an oil-filled reactor or the like.
2. Description of Related Art
The life of an oil-filled electric apparatus such as an oil-filled transformer, an oil-filled reactor or the like is generally estimated from the degree of deterioration of the insulating paper used therein. The degree of deterioration of the insulating paper is determined by measuring its tensile strength, the degree of polymerization thereof and the like. Investigation is increasingly made as to whether or not deterioration of such insulating paper can be diagnosed by measuring the deterioration products, ex. furans such as furfural, furancarboxylic acid and the like, and aldehydes such as acetoaldehyde, formaldehyde and the like.
However, the measurement of the degree of deterioration of insulating paper by measuring its tensile strength and the degree of polymerization thereof is limited to the opportunity for internal inspection which allows the insulating paper to be collected from an oil-filled electric apparatus. On the other hand, as the insulating paper decomposes, furfural (also referred to as furaldehyde) is produced and dissolves in insulating oil. Since the amount of furfural dissolved in the insulating oil can be measured by collecting the insulating oil, there is the advantage that the life of the oil-filled electric apparatus can be diagnosed during the operation thereof. However, it has become clear that the furfural produced from the insulating paper used in the oil-filled electric apparatus not only dissolves in the insulating oil but also is well adsorbed on the insulating paper, as described below. This led to the finding that the total amount of furfural cannot be measured by analyzing only the furfural dissolved in the insulating oil.
Since this finding has previously not been taken into account, there has been the following problem: If the degree of deterioration of insulating paper is diagnosed from the analytical result of furfural dissolved in insulating oil, the calculated amount of furfural produced is smaller than the actual furfural amount by the amount of furfural adsorbed on the insulating paper. This results in poor precision of diagnosis of the life of the apparatus.